1. Field of the Invention
The present invention relates to an imprint apparatus, and a pattern transfer method using the imprint apparatus.
2. Description of the Related Art
Imprint technique makes it possible to transfer nanoscale micropatterns, and is beginning to be put into practical use as one nanolithography technique for the mass-production of magnetic recording media and semiconductor devices. In the imprint technique, a mold having a micropattern is used as an original to form the micropattern on a substrate such as a silicon wafer or glass plate by using an apparatus such as an electron-beam exposure apparatus. The micropattern is formed by coating the substrate with a resin (dispensing a resin on the substrate), and curing the resin while the pattern of the mold is pressed against the substrate with the resin being sandwiched between them. Imprint techniques presently put into practical use are the heat cycle method and photo-curing method. The heat cycle method forms a pattern by increasing the fluidity of a thermoplastic resin by heating the resin to a temperature greater than or equal to the glass-transition temperature, pressing a mold against a substrate with the resin having a high fluidity being sandwiched between them, and releasing the mold from the resin after cooling. The photo-curing method forms a pattern by pressing a mold against a substrate with an ultraviolet-curing resin being sandwiched between them, curing the resin by irradiating it with ultraviolet light in this state, and releasing the mold from the cured resin. In the heat cycle method, the transfer time increases due to temperature control, and the dimensional accuracy decreases due to temperature changes. However, the photo-curing method has no such problems. Presently, therefore, the photo-curing method is advantageous in the mass-production of nanoscale semiconductor devices.
Various imprint apparatuses have been implemented in accordance with resin curing methods and applications. As an apparatus for mass-producing semiconductor devices and the like, an apparatus using step and flash imprint lithography (SFIL) is effective. An imprint apparatus fitted for SFIL is disclosed in Japanese Patent No. 4185941. This imprint apparatus includes a substrate stage, a resin coating mechanism, an imprint head, a light irradiation system, and a mechanism for detecting a positioning mark. To perform measurement for aligning a substrate with a mold, the imprint apparatus as described above adopts a so-called die-by-die method in which marks formed on the substrate and mold are optically simultaneously observed for each shot when pressing the mold against the substrate, and a resin is cured by correcting the displacement amount.
In the die-by-die method, however, the overlay accuracy changes from one shot to another, so the product performance must be confirmed. This makes it necessary to test the product performance for all shots in a post-process. Also, performing alignment for each shot takes a long time, and decreases the productivity. Accordingly, the global alignment method is currently most frequently used. In this method, marks of several typical shots are measured, and statistical processing is performed based on the measurements, thereby molding all shots by using the same index. Since the global alignment method performs molding by using the same index, the quality of all shots of a substrate can be determined by conducting a sampling test on a few shots in a post-process. This increases the productivity. Furthermore, in the global alignment method, a substrate is fed under a mold and pressed based on measurement results. Therefore, it is necessary to stably and accurately detect the relative positions (a so-called baseline amount) of the mold and a detection system for observing the substrate. The accuracy is normally ensured by measuring the baseline amount every predetermined time.